AIM: The aim of this research is to measure for the first time IN VIVO, using non-invasive methods developed by us, the elasticity of cortical bone, and the trabecular bone mineral density of three groups of patients, all with a common bone problem OSTEOPOROSIS. The groups of patients furnished by our clinical colleagues who are co-investigators are 1) children with Turner's Syndrome (gonadal dysgenesis), 2) female athletes undergoing severe endurance training who develop amenorrhoea and subsequently osteoporosis with fractures, 3) patients with postmenopausal and senile osteoporosis and osteoprososis of disuse following traumatic paraplegia. In Turner's syndrome the investigation will help evaluate the effects of drug therapy, and help categorize the growth disorder of children. In the female athletes the investigation will help identify those at risk before fracture occurs. In established osteoporosis (postmenopausal, etc.) the investigation will for the first time give the clinician an objective index of the effects of different treatment regimes. Hitherto the only useable measurement has been the bone mineral content (BMC), but experience shows this to be too insensitive. BMC will be measured but mainly for comparison purposes. METHODOLOGY: The measurement of elasticity of bone is made by measuring the speed of sound in the cortex of the proximal radius. The measurement of trabecular bone mineral density is made by measuring the ratio of coherent to Compton scattered photons from the trabeculae of the calcaneum. Both methods are fully validated and already reported in the literature. CONCLUSION: Osteoporosis is a loss of bone, resulting from many causes at all ages. It leads to fracture with miminal trauma and is therefore costly in terms of human suffering and health care resources. Hitherto the condition could not be accurately measured. We now have the methodology to do this and pilot projects have convinced the clinicians concerned that they can now start to obtain the information needed to make rational decisions about their patients.